Secondary batteries such as lithium ion secondary batteries have characteristics such as compact size, light weight, high energy-density, and the ability to be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, studies have been carried out in recent years with the objective of further raising the performance of secondary batteries through improvement of electrodes and other battery components.
An electrode used in a secondary battery such as a lithium ion secondary battery normally includes a current collector and an electrode mixed material layer (positive electrode mixed material layer or negative electrode mixed material layer) formed on the current collector. This electrode mixed material layer is formed by, for example, applying a slurry composition containing an electrode active material, a binder-containing binder composition, and so forth onto the current collector, and then drying the applied slurry composition.
In order to further improve the performance of secondary batteries, attempts have been made in recent years to improve binder compositions used in electrode mixed material layer formation.
In one specific example described in PTL 1, a binder composition containing a rubber polymer, such as acrylate rubber, that has a polymethylene-type saturated main chain and does not contain fluorine atoms and a non-aromatic organic compound solvent having a carbon number of 2 to 20 and a boiling point of 85° C. to 350° C. is used to enable strong adherence between an electrode active material and a current collector, and to improve secondary battery cycle characteristics.
In another example described in PTL 2, a binder composition that contains a mixture of a fluororubber and a hydrogenated nitrile rubber as a binder is used to improve secondary battery cycle characteristics.